I still don't see 'wild variations', but I do see some minor differences, within the tolerances of the specs, on the MkXIIs, and I also see staining and dirt, and shadow and photo highlights 'burning out' some demarcations in the second pic. The gate guard can be discounted, as, at that particular period, they could be painted in an approximation, having most likely been previously silver doped overall, as Instructional Airframes.
The pic showing the application of the AEAF stripes also shows the standard camouflage pattern, although granted with heavy exhaust staining obscuring some of the colours, and also dirt.
These stripes were very hastily applied on the evening of June 4th, following orders to delay until evening, so that it was done a few hours before what should have been 'D-Day' which, as we all should know, was postponed for 24 hours due to bad weather. The 'paint' used was a water-based, 'washable' distemper -type emulsion, ans as there were so many aircraft on each forward operating strip along the south of England, accuracy in application was not a crushing concern, and many were painted by whichever personnel were available, including Army.
No one is saying that every Spitfire was absolutely identical in its paint finish, but they certainly were not 'wildly varied and, if a modeller wants to be 100% accurate, which is probably impossible, then he or she needs to study every available image of the actual subject aircraft, replicating the paint scheme, pattern and shades, and any weathering and staining, the latter being a totally different matter, compared to variations in pattern.